The invention concerns a loop buffer with variable loop length for a conveyor for strip material. More particularly, the invention relates to a loop buffer for continuous strips of film material made up of individual sections. The loop buffer includes a deflector roll on each of input and output sides, powered if appropriate, and a loop roll flexibly mounted between them in a vertical direction, the height of which relative to the deflector rolls determines the loop length.
Loop buffers of this type are used in strip conveyors to decouple asynchronous conveyor speed at various stations in the conveyor system. One typical application is machines for processing photographic material, normally called printers, where the speeds of the various processing stages vary greatly. There are some sections where the strip material is advanced continuously in a substantially uniform manner, and other sections (e.g. the notching station and the exposure station) where the strip material is conveyed in larger or smaller steps.
Loop buffers of this general type hitherto disclosed have a relatively heavy loop roll, or one which is held down by a spring, with the spring extending over the whole travel of the loop roll. The loop roll is mounted on a weighted pivoting lever as disclosed in DE-A-22 27 995. The loop roll is weighted or spring-tensioned to ensure positive feeding of the strip material. In practice these loop buffers generate severe impacts and tension peaks in the strip material when the strip advance changes speed abruptly or drastically, as happens for example with intermittent advance, and these peaks and impacts constitute a serious danger of damage to the strip material, and/or lead to faults in the neighboring stations, and are therefore highly undesirable.